1. Field of the Invention
The present invention relates to a two-cycle internal combustion engine capable of preventing blow-by of an air-fuel mixture in an internal combustion engine and thereby enhancing the combustion stability, fuel economy and exhaust purifying performance. More particularly, the invention is concerned with a two-cycle internal combustion engine wherein in a communication passage between a combustion chamber and a chamber portion adjacent thereto is disposed a control valve for controlling the communication passage to open and close the same passage, and through the communication passage a fuel or an air-fuel mixture is supplied or charged into the combustion chamber and a highly compressed gas is supplied or charged into the chamber portion. In particular, the shape and position of the communication passage and the control valve are optimized to render the communication passage and the control valve more effective.
2. Description of Background Art
In the conventional two-cycle internal combustion engine, fuel supplied from a carburetor is mixed with intake air. The resulting mixture is introduced into a crank chamber and is thereafter supplied into a combustion chamber through a scavenging port. An opening timing of an exhaust port is set earlier than that of the scavenging port (the upper edge of the exhaust port is higher than that of the scavenging port), so that as the air-fuel mixture fed into the combustion chamber is discharged to an exhaust passage, thus, a so-called blow-by is apt to occur.
The blow-by is suppressed by an exhaust pulsating effect of the exhaust chamber, but throughout the whole operation area it is difficult to effect such suppression. This difficulty exerts an influence on both fuel economy and exhaust purifying performance.
In an effort to solve this problem, a two-cycle internal combustion engine, as disclosed in Japanese Patent Laid Open Nos.100318/91 and 302521/93, has been proposed.
In the two-cycle internal combustion engine disclosed in the patent laid open No.100318/91, a high pressure chamber is connected to a crank chamber through a check valve, the high-pressure chamber and a combustion chamber are connected with each other through an air passage. A solenoid valve is disposed at the lower end of the air passage, while at the upper end of the air passage is disposed a fuel injection valve capable of injecting fuel into the combustion chamber.
In the two-cycle internal combustion engine disclosed in Japanese patent laid open No.302521/93, a chamber is formed adjacent both the crank case and cylinder block. An intake control valve is disposed between a crank chamber and said chamber. A scavenging control valve is disposed between the chamber and a combustion chamber in a cylinder. In addition, a fuel injection valve is provided for injecting fuel into the said chamber.
In the two-cycle internal combustion engine disclosed in the patent laid open No.100318/91, however, since a fuel supply port is formed in the side wall of the cylinder and the fuel injection valve is located perpendicularly toward the port, the fuel spray strikes against the cylinder wall on the exhaust port side and is apt to adhere thereto.
If the spray timing is quickened so as not to cause interference of the fuel spray with the piston, blow-by of the fuel spray to the exhaust port is apt to occur. Conversely, if the port for the supply of fuel is formed at a high position for delaying the spray timing, the fuel injection valve is exposed to high temperature combustion gas and is thus required to have a high heat resistance.
In the two-cycle internal combustion engine disclosed in the patent laid open No.302521/93, since the air-fuel mixture injected from the scavenging control valve is fed into the combustion chamber through all of scavenging ports, blow-by of the mixture from the exhaust port is unavoidable.
The Assignee of the present invention has previously filed Japanese Patent Application No. 269366/96 for a two-cycle internal combustion engine solving the above-mentioned problems of the prior art.
According to the Application No. 269366/96, in a two-cycle internal combustion engine wherein a control valve for controlling the communication passage to open and close the same passage is positioned in a communication passage between a combustion chamber and a chamber formed sideways of the combustion chamber and connected to a fuel injection device. Through the communication passage fuel is supplied or charged into the combustion chamber, while a highly compressed gas is supplied or charged into the chamber formed sideways of the combustion chamber. The communication passage includes a first communication passage through which the highly compressed gas flows from the combustion chamber to the chamber formed sideways of the combustion chamber and a second communication passage through which an air-fuel mixture flows from the chamber to the combustion chamber. The control valve includes a first control valve disposed in the first communication passage and a second control valve disposed in the second communication passage. The first control valve causes the first communication passage to open at a timing near closing of an exhaust port and causes it to close halfway in a compression stroke, while the second control valve causes the second communication passage to open at a timing near closing of a scavenging port and causes it to close before closing of the first communication passage.
Since the above two-cycle internal combustion engine filed by the Assignee of the present invention is constructed as above, scavenging with air alone is performed at the initial stage of scavenging, whereby the blow-by, namely passage of the air-fuel mixture as it moves through the combustion chamber and discharge thereof to the exhaust passage, is prevented. Besides, the fuel (rich mixture) fed into the combustion chamber is mixed with the air into a mixture of an appropriate concentration within the combustion chamber because the interior of the same chamber has been scavenged sufficiently with the air, thus affording a satisfactory combustion. Consequently, a high level of fuel economy and a high exhaust purifying performance can be attained.
Moreover, since the charging of the highly compressed gas into the chamber formed sideways of the combustion chamber is performed through the first communication passage from the combustion chamber in the compression stroke, an almost constant high pressure in the combustion chamber can be utilized for the charging of the gas. In comparison with the conventional gas charging which utilizes the internal pressure of the crank chamber, the drop of pressure caused by a full opening of the throttle valve with increases the number of revolutions of the engine is not influential at all, so there is obtained a more certain and stable, high chamber pressure (see FIGS. 9 and 10).
Further, since the highly compressed gas for creating a rich air-fuel mixture is obtained from the combustion chamber, the control valve (a rotary valve) disposed in the communication passage for communication between the combustion chamber and the chamber formed sideways of the combustion chamber can be mounted in the cylinder-wall located near the combustion chamber. As a result, the length of the communication passage between the control valve and a mixture injection port (a combustion chamber-side port of the second communication passage) can be shortened, whereby the amount of air required for moving the mixture through the communication passage can be decreased.
In addition, the time required for the fuel to move through the communication passage is shortened and the influence of the time factor on the setting of an opening timing of the control valve is diminished, so that it becomes easier to set the control valve opening timing, and the opening timing once set is easy to cover a wide range of engine revolutions.
Thus, the two-cycle internal combustion engine invention filed previously by the Assignee of the present invention can bring about various effects, but in order to make these effects more outstanding, there have still been points to be optimized with respect to the shape and position of the communication passage for communication between the combustion chamber and the chamber formed sideways of the combustion chamber, as well as the shape and position of the control valve disposed in the communication passage.